1. Field of the Invention
The present invention relates to semiconductor laser diodes capable of light emission at a single wavelength in the visible range, particularly from the blue to the violet range, as well as in the ultraviolet range, and a method for producing group III nitride compound semiconductor lasers.
2. Description of Background Information
The laser diode proposed in Unexamined Japanese Patent Publication (kokai) Hei-4-242985 is fabricated from gallium nitride based compound semiconductors ((Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y N; 0.ltoreq.x.ltoreq.1; 0.ltoreq.y.ltoreq.1), with the active layer being undoped with impurities.
Furthermore, that reference discloses group III nitride compound semiconductor lasers fabricated by creating p-type conduction in (Al.sub.x Ga.sub.y In.sub.1-x-y N; including the cases of x=0, y=0 and x=y=0) through exposure to electron beams. Such semiconductor lasers have an AlN buffer layer formed on a sapphire substrate which, in turn, is overlaid with a pn heterojunction in a group III nitride compound semiconductor (Al.sub.x Ga.sub.y In.sub.1-x-y N; including the cases of x=0, y=0 and x=y=0).
This laser diode is fabricated by epitaxial growth of a gallium nitride compound semiconductor on a sapphire substrate. For the manufacture of reliable laser diodes, it is necessary to provide precise mirror surfaces; however, no one has ever succeeded in finding the directions of cleavage capable of providing precise mirror surfaces.
Furthermore, these lasers require cleaving of not only the group III nitride compound semiconductor laser elemont layers but also of the sapphire substrate. However, it is difficult to cleave the sapphire substrate per se; additionally, the 30.degree. offset between the A axis of sapphire and that of the group III nitride compound semiconductor makes it impossible to create cleavage surfaces of high quality in the group III nitride compound semiconductor laser element layer.